Ribosomes are macromolecular structures that catalyze protein synthesis in cells. They consist universally of two subunits composed of numerous proteins and several RNAs. Proteins contribute to the structure, stability, and activity of the subunits. However, in general, it has been difficult to assign specific functions to individual ribosomal proteins, as many are not essential for ribosomal function or have additional extraribosomal functions. By contrast, ribosomal RNAs (rRNAs) are responsible for the overall shape of the ribosomal subunits as well as for the enzymatic activity that catalyzes protein synthesis. Evidence is accumulating that rRNAs may also affect other aspects of protein synthesis, including mRNA recruitment, regulation of the efficiency of translation of specific mRNAs, and facilitation of ribosomal shunting.
The ability to study the role of rRNA in ribosome assembly, protein synthesis, and non-canonical aspects of rRNA function requires being able to alter rRNA sequences and monitor the activity of modified ribosomal subunits in vivo. Analysis of rRNA processing, ribosome assembly, and function of higher eukaryotic rRNA have been hindered by the lack of an expression system that enables rRNA to be modified and then examined functionally.
There is a great need in the art for effective systems for expressing modified rRNAs and performing functional analyses, especially mammalian systems.